1. Field of the Invention
This invention relates to apparatus and methods for the disinfection of fluids and, in particular, to exposing fluids to magnetic fields and ultraviolet radiation.
2. Description of the Background
Industrial fluids such as machine tool coolants, cooling tower water and organic lubricants traditionally possess fairly short useful lives. Microbial contaminants find their way into these fluids and proliferate. Microorganisms feed on fluid components as well as contaminants that leak into the fluid. As the microorganisms flourish, the fluid becomes even more inviting to further growth as generation after generation of microbes degrade essential components of the fluid, and add even more organic nutrients to the fluid. This process of degradation creates noxious odors in the environment.
In an attempt to deal with this problem, biocides are added to fluids in an effort to destroy microorganisms or hinder microbial growth. These chemicals are quite toxic to humans and can quickly build up to toxic levels making repeated treatments impractical. Useful life for such fluids is only slightly extended. In addition, there are considerable environmental problems associated with disposal of contaminated and biocide-treated fluids, due in large part to the presence of the additives and contaminants. At present, fluid supplies tend to require frequent replacement.
Industrial fluids were commonly discarded by dumping in drains, sewers and rivers, causing extensive and prolonged environmental impact. In 1976, the EPA ruled that fluids such as oil-based coolants were contaminated waste and must be treated or a new way of disposal found (Public Law 94-580; Oct. 21, 1976). To meet this directive, centrifugation or filtration were considered as the primary choices for selective removal of contaminants. Filtration, although useful for removing certain contaminants, fails to remove others. Further, filters often clog or break requiring more overall costs than would have been incurred by complete fluid replacement. Centrifugation, the principal means for removing contaminated oils in coolant fluids found in larger machine tool plants, has a limited treatment rate. Similarly, cyclonic separators, in which the fluid is spun, are not able to remove all of the contaminants. Design limitations prevent reduction of contaminant concentration to no less than about two percent on a practical basis. This partial removal does not prevent bacterial regrowth or breakdown of coolant and oil components. Consequently, successful filtration and centrifugation processes, while essential for recycling for useful processing operations, only prolong the life of the fluid by a few weeks.
Ultraviolet (UV) treatment has been used to disinfect clear waters and some wastewater as described in U.S. Pat. Nos. 3,634,025; 3,700,406; 3,837,800; 3,889,123, 3,894,236; 4,471,225 and 4,602,162. Each of these U.S patents describes a method touted to be designed to sterilize water-based fluids. The principal idea behind this technique was that UV radiation would penetrate the clear liquid to kill offending microorganisms. The conventional technology of UV treatment is limited because total quartz systems have a tendency to foul easily and maintenance costs were high. UV treatment proved to be unsuccessful for industrial fluids such as coolants, as coolants are opaque, or substantially so, and often contain significant levels of contaminants such as hydraulic and way oils and ferric compounds and complexes which are highly occlusive to ultraviolet light. Under these constraints, ultraviolet radiation cannot pass more than a very small distance, if at all, into the fluid stream (e.g. U.S. Pat. No. 3,456,107). These contaminants and coolants blocked UV transmission directly and also indirectly by adhering to wall surfaces of submerged quartz UV lamps or to the inner surfaces of the UV transmissible tubing in a dry system design, wherein UV lamps are kept separated from the fluid being treated.
A number of measures to prevent the degradation of industrial fluids by microorganisms have been attempted with the objective of prolonging the life of the fluid and reducing odors and health risks associated with fluid spoilage. To minimize these risks and the hazards of contaminated coolant fluids, many facilities add appreciable levels of various biocide fluids to kill and inhibit the growth of microorganisms (e.g. U.S. Pat. No. 3,230,137). In general, coolants and other fluids perform properly in the presence of these additives. However, people exposed to biocides commonly experience allergic reactions. In many cases, the biocides interacted with the skin of workers and caused various forms of hypersensitivity and dermatitis. In short, although bacterial counts can be reduced over the short term, biocides were often more problematic than the microorganisms themselves. Ultimately, the microorganisms overcome the biocides and the microbial degradation of coolant components and contaminants results in foul odors in the work environment.
Most conventional techniques, although useful in the short term, do not provide long term reduction of microbial counts in large industrial systems by more than a single log and, more importantly, only prolong coolant life for a short period despite their high cost. Other techniques such as aeration of the fluid and thorough cleaning of the lines and machines through which the coolant flows proved to be largely unsuccessful in maintaining low levels of bacterial populations. Bacteria regrow in this environment due to the presence of available nutrients, and overcome inhibitory factors introduced by aeration or chemical management. Ultimately, the bacteria take hold growing as biofilms that can produce scale deposits throughout the fluid containment and delivery system.
Other methods for the disinfection of industrial fluids include pasteurization. In this process, fluids are heated to a pasteurizing temperature for a required period of time and subsequently cooled to an operating temperature. This process is energy intensive and the costs, resulting from the heating and cooling steps, are high. Although attempts have been made to keep pasteurization temperatures below critical temperatures that destroy or denature the industrial fluids, constant temperature cycling negatively effects many of the chemicals found in the fluid. Consequently, there is a strong need for a safe and environmentally friendly method for the disinfection of industrial and other fluids.
Another problem with fluids, although not particularly coolant fluids, is the build-up of deposits in and along the walls that confine and guide the fluid along a particular path. Deposits in water-based fluids that are the most concern seem to be calcium in the form of lime, a combination of calcium oxide and calcium hydroxide, or other forms of calcium such as calcium carbonate, calcium sulfate and calcium phosphate. Scale also includes other elements such as magnesium hydroxide, zinc phosphate, sodium salts and various forms of iron oxides and silicates.
Scaling causes decreased heat transfer efficiency in, for example heat exchange systems such as radiators and cooling towers. Scaling can also seriously elevate temperatures within a scaled tube and cause over-heating of elements within a fluid system. The build-up of scale also leads to lower storage capacities in scaled tanks and reduced or complete blockage of fluid passage necessitating large costs for scale removal. These costs are often so high or the materials so damaged that complete replacement is often necessary.
Scale and other types of deposits can be corrosive to pipes and other surfaces within the fluid stream. Corrosion can be divided into at least eight unique forms, each with its own causes and effects which includes uniform corrosion, galvanic or two metal corrosion, crevice corrosion, pitting corrosion, intergranular corrosion, selective leaching, erosion corrosion and stress corrosion. The chemical constituents of the fluid on the system have a great influence on the type and extent of corrosion. An increased salt content, such as sodium, is well know to be strongly corrosive even to the most corrosion resistant materials. Scale serves as a habitat for bacteria in the fluid containment and delivery system and provides an ideal location for replication and subsequent formation of biofilms.
Attempts have been made for many years to prevent corrosion and scaling by treating the pipes themselves. In many cases, pipes would be machined to nearly absolute smoothness so that there were few places for deposits to take hold and collect. By reducing these sites it was believed that corrosion and scale formation could be significantly reduced. Alternatively, chemical compounds such as, for example, acids could be added to the fluid to prevent scaling and unwanted precipitation. However, many of these chemical compounds were damaging to the fluid or would effect subsequent use of the fluid and could not be utilized. Still other types of fluids could not be treated at all, either because the additives were harmful to the user or to the fluid itself.
Conventional methods for the control of scale formation within a system required control over solubility and nucleation and crystal growth within the fluid within the system. Acid treatment and ion exchange, two of the more common approaches, are designed to control solubility by preventing the formation of supersaturated solutions while others, including chemical inhibitors, control nucleation and crystal growth.
One of the more controversial methods for the prevention of scale and corrosion involves passing the fluid through an applied field (e.g. electrostatic, magnetic, electromagnetic). Since the 1950's, a large number of claims have been made as to why and how magnetic fields can reduce corrosion and scale formation in water-based fluids. For example, the magnetic treatment has been celebrated to reduce nucleation rates, alter the structure of crystals intimately involved with deposits, increase coagulation tendencies and reduce crystallization. Magnetic fields have also been purported to reduce precipitation rates, increase coagulation and alter the kinetics of crystal growth. Other studies have shown that magnetic water treatment produces no change to fluid conductivity, no change in material solubility and no changes in fluid pH. These reports have yet to be unscrambled scientifically. However, there do appear to be a number of real effects including reduced scaling and reduced corrosion.
The effects of magnetic treatment can be both immediate and long term. Immediate effects include reduced scaling while the magnetic field is being applied. Long-term effects, or memory, have also been observed in fluid after the magnetic field has been turned off. Scale accumulation and corrosion remain reduced for hours and sometimes days. The scientific explanation for this may be related to the rate of crystal formation. Calcium carbonate is found in at least two thermodynamic forms, the more stable calcite crystal which easily precipitates and the unstable argonite/vaterrite crystal which resists precipitation. Over time, thermodynamic considerations favor formation of calcite crystals and, thus, precipitation. Magnetic treatment favors formation of the less stable argonite/vaterrite crystals and thus, less precipitation. Once magnetic treatment has ended a period of time is required for the existing, unstable crystals to transition into the more stable calcite crystals. Thus imparting the memory effect.
Although applied fields, including magnetic treatment, have produced some level of success, microorganisms and deposits still exist as a problem in the industry.